Buggy code:
public class TextViewer extends JPanel implements Observer , CaretListener , IMimePartViewer { private static final Logger LOG = Logger . getLogger ( "org.columba.mail.gui.message.viewer" ) ; private static final Pattern CIDPattern = Pattern . compile ( "cid:([^\"]+)" , Pattern . CASE_INSENSITIVE ) ; private String css = "" ; private XmlElement smilies ; private boolean enableSmilies ; private String name ; private String body ; private boolean htmlMessage ; private MessageController mediator ; private IHTMLViewerPlugin viewerPlugin ; private IMailbox folder ; private Object uid ; private boolean usingJDIC ; public TextViewer ( MessageController mediator ) { } private void initHTMLViewerPlugin ( ) { } private IHTMLViewerPlugin createHTMLViewerPluginInstance ( String pluginId ) { IHTMLViewerPlugin plugin = null ; try { <START_BUG> IExtensionHandler handler = PluginManager . getInstance ( ) . getHandler ( ORG_COLUMBA_CORE_HTMLVIEWER ) ; <END_BUG> IExtension extension = handler . getExtension ( pluginId ) ; if ( extension == null ) return null ; plugin = ( ( IHTMLViewerPlugin ) ( extension . instanciateExtension ( null ) ) ) ; return plugin ; } catch ( PluginHandlerNotFoundException e ) { TextViewer . LOG . severe ( ( "Error<seq2seq4repair_space>while<seq2seq4repair_space>loading<seq2seq4repair_space>viewer<seq2seq4repair_space>plugin:<seq2seq4repair_space>" + ( e . getMessage ( ) ) ) ) ; if ( Logging . DEBUG ) e . printStackTrace ( ) ; } catch ( PluginException e ) { TextViewer . LOG . severe ( ( "Error<seq2seq4repair_space>while<seq2seq4repair_space>loading<seq2seq4repair_space>viewer<seq2seq4repair_space>plugin:<seq2seq4repair_space>" + ( e . getMessage ( ) ) ) ) ; if ( Logging . DEBUG ) e . printStackTrace ( ) ; } catch ( Exception e ) { TextViewer . LOG . severe ( ( "Error<seq2seq4repair_space>while<seq2seq4repair_space>loading<seq2seq4repair_space>viewer<seq2seq4repair_space>plugin:<seq2seq4repair_space>" + ( e . getMessage ( ) ) ) ) ; if ( Logging . DEBUG ) e . printStackTrace ( ) ; } return null ; } private void initConfiguration ( ) { } public void view ( IMailbox folder , Object uid , Integer [ ] address , MailFrameMediator mediator ) throws Exception { } private boolean isHTMLStrippingEnabled ( ) { } private void initStyleSheet ( ) { } public void update ( Observable arg0 , Object arg1 ) { } public String getSelectedText ( ) { } public JComponent getView ( ) { } public void updateGUI ( ) throws Exception { } public void caretUpdate ( CaretEvent arg0 ) { } private String downloadCIDParts ( String body , MimeTree mimeTree ) { } private MimePart findMimePart ( List mimeParts , String findCid ) { } private void downloadMimePart ( MimePart part , File destFile ) throws Exception { } public boolean isHtmlMessage ( ) { } protected void processPopup ( MouseEvent ev ) { } protected URL extractURL ( MouseEvent event ) { } private ColumbaURL extractMailToURL ( MouseEvent event ) { } class URLMouseListener implements MouseListener { public void mousePressed ( MouseEvent event ) { } public void mouseReleased ( MouseEvent event ) { } public void mouseEntered ( MouseEvent event ) { } public void mouseExited ( MouseEvent event ) { } public void mouseClicked ( MouseEvent event ) { } } }

Fix:
IExtensionHandler handler = PluginManager . getInstance ( ) . getExtensionHandler ( ORG_COLUMBA_CORE_HTMLVIEWER ) ;